The very large numbers of ‘channels’ output to terrestrial, satellite and cable distribution systems by typical broadcasters cannot be monitored economically by human viewers and listeners. And, audio visual content, such as films, television shows and commercials received from content providers cannot always be checked for conformance with technical standards by human operators when ‘ingested’ into a broadcaster's digital storage system. The historic practice of checking by a person who looks for defects and non-conformance with standards is no longer economic, or even feasible, for a modern digital broadcaster.
These developments have led to great advances in automated quality checking (QC) and monitoring systems for audio visual content. Typically QC and monitoring equipment analyses audio visual data using a variety of different algorithms that identify specific characteristics of the content such as:                Audio dynamic range        Duration of periods of silent audio or black video        Presence of subtitles        Presence of test signals        Video aspect ratio and presence or absence of ‘black bars’ at the edges of the video frame        Audio to video synchronisation        
The results of this analysis may be stored as ‘metadata’ that is associated with the audio visual content; or, it may be used in a monitoring system that detects defects in distributed content and alerts an operator, or automatically makes changes to signal routing etc. to correct the defect.
Typical QC and monitoring processing is complex, and the resulting volume of metadata is large. QC equipment is therefore usually placed at only a few points in a distribution or processing system, perhaps only at the system's input and output points.